1. Field of the Invention
The present invention relates to a dielectric microwave filter; and, more particularly, to a dielectric microwave filter, having a miniaturized structure but increased performance and which effectively modulates coupling of electromagnetic fields between input/output terminals and a resonator, and which can be manufactured in an easy and simplified manner.
2. Description of the Prior Art
In general, a dielectric microwave filter includes a dielectric coaxial resonator of TEM mode, wherein the number of the dielectric coaxial resonators is determined by the desired properties of the dielectric microwave filter, and at least two dielectric coaxial resonators are required to form a dielectric microwave filter.
In FIGS. 1 and 2, there are provided schematic perspective views of dielectric microwave filters previously disclosed.
In FIG. 1, there is presented a schematic perspective view of a dielectric microwave filter in accordance with one embodiment of the prior art.
The dielectric microwave filter includes a dielectric body 1, a plurality of resonators 2, apertures 3, dielectric members 4 and conductive sticks 5, wherein the dielectric body 1 has a top surface 1', and the resonators 2 have parallel axes.
A trinity of first, second and third parallel resonators 2, a pair of apertures 3, a pair of dielectric members 4 and a pair of conductive sticks 5 are provided in the dielectric microwave filter of FIG. 1.
Each of the resonators 2 extends from the top surface 1' of dielectric body 1 to the bottom of dielectric body 1, and has an inner surface coated with an electrically conducting material, e.g., Au, thereby allowing it to be operated as a resonator having a quarter wavelength.
Each of the conductive sticks 5 is inserted into the first and the third resonators 2 in the dielectric body 1 with a dielectric member 4 intervening therebetween, and functions as an input/output terminal. The dielectric member 4 joins conductive stick 5 and resonator 2.
Each of the apertures 3 is located between the resonators 2, thereby modulating coupling of electromagnetic fields between the resonators 2, and is parallel with the resonators 2.
An electrically conducting material, e.g., Au, completely covers all surfaces of the dielectric microwave filter, except for an inner surface of each of the apertures 3 and the top surface 1' of the dielectric body 1.
In the above-described dielectric microwave filter, an electrical signal is applied to the conductive stick 5 inserted into the first resonator 2, which functions as an input terminal, and is, then, transmitted to the first resonator 2 by coupling of electromagnetic fields therebetween, to transmit an electrical signal from the first resonator 2 to the third resonator 2 by coupling of electromagnetic fields among the resonators 2, wherein the electrical signal transmitted from the first resonator 2 to the third resonator 3 is selectively attenuated by each of the apertures 3.
Thereafter, the electrical signal transmitted from the first resonator 2 to the third resonator 2 is applied to conductive stick 5 inserted into the third resonator 2, which functions as an output terminal.
In FIG. 7 there is shown a schematic diagram of the dielectric microwave filter shown in FIG. 1.
The coupling of electromagnetic fields between the resonators (102) having a quarter wavelength is represented by comb lines 104, and each of the resonators (102) is electrically connected to ground. The connection of an input/output terminal and the resonators (102) using the coupling of electromagnetic fields therebetween is represented by capacitances 103.
In the above-described dielectric microwave filter, the coupling of electromagnetic fields among the resonators 2 is decreased by increasing the size of each of the apertures 3 formed between the resonators 2. Furthermore, the coupling of electromagnetic fields among the resonators 2 is also determined by changing the position of each of the apertures 3 between the resonators 2.
There are certain deficiencies associated with the above-described dielectric microwave filter. Since the size and the position of each of the apertures 3 formed between the resonators 2 are limited within the finite dielectric body 1, the control of coupling of electromagnetic fields among the resonators 2 also encounters limitations, and it is also difficult to manufacture the dielectric microwave filter in miniaturized size.
Furthermore, during manufacture of the dielectric microwave filter, since all surfaces thereof, except for an inner surface of each of the apertures 3 and the top surface 1' of the dielectric body 1 are completely covered with an electrically conducting material, e.g., Au, removal of the electrically conducting material formed on the inner surface of each of the apertures 3 and the top surface 1' of the dielectric body 1 is required during manufacture. This may further compound the already complicated overall manufacturing process of the dielectric microwave filter.
In addition to the above described deficiencies in manufacture, the dielectric microwave filter thus prepared has a major shortcoming in that transmission of an electrical signal may occur through the electrically conducting material coated thereon, not through the resonators 2, which will, in turn, degrade the overall desired performance of the dielectric microwave filter.
In FIG. 2, there is presented a schematic perspective view of a dielectric microwave filter in accordance with another embodiment of the prior art.
The dielectric microwave filter of FIG. 2 includes a dielectric body 1a, a plurality of resonators 2a, grooves 6, dielectric members 4a and conductive sticks 5a, wherein the dielectric body has a top surface 1'a and front and rear surfaces, and the axes of each of the resonators 2a are parallel with each other.
A trinity of first, second and third parallel resonators 2a, two pairs of grooves 6, a pair of dielectric members 4a and a pair of conductive sticks 5a are included in the dielectric microwave filter of FIG. 2.
Each of the resonators 2a extends from the top surface 1'a of the dielectric body 1a to the bottom of the dielectric body 1a.
Each of the conductive sticks 5a is inserted into the first and the third resonators 2a in the dielectric body 1a with the dielectric member 4a intervening therebetween to function as an input/output terminal. The dielectric member 4a joins conductive stick 5a and resonator 2a.
Each pair of grooves 6 is located on the front and rear surfaces of dielectric body 1a, wherein each of grooves 6 is positioned between resonators 5a, thereby modulating the coupling of electromagnetic fields between parallel resonators 2a.
In the above-described dielectric microwave filter, since the dielectric body 1a has two pairs of grooves 6 formed on the front and the rear surfaces instead of having a pair of apertures formed therein, the dielectric microwave filter could be manufactured in an easier and simplified manner. There are still certain deficiencies associated with this dielectric microwave filter, however. Since the electromagnetic fields at a center portion of the dielectric body 1a are larger than at front and rear portions thereof, modulation of the coupling of electromagnetic fields by using the two pairs of grooves 6 is relatively low.
Furthermore, an input electrical signal may also be transmitted through an electrically conducting material coated thereon, which will, in turn, degrade overall performance of the dielectric microwave filter.